The objective of the study is to define the human thorax in a quantitative statistical manner such that the information will be useful to the designers of cardiac prostheses, both total replacement and assist devices. This information will also be clinically useful in that the proposed recipient of a cardiac prosthesis can by simple radiography be assured of an adequate fit with the prosthesis prior to the implantation. Data used in this study is obtained from a number of sources. Previously we obtained thoracic molds made from human cadavers, chest radiographs of normal adults, published anatomy data, and angiograms of patients with cardiac disease. The most accurate data being obtained at present is from computerized axial tomography (CAT) of the human thorax in living patients.